The present invention relates to the radiographic arts. It finds particular application in conjunction with computerized tomographic (CT) scanners and will be described with particular reference thereto. However, it is to be appreciated that the present invention will also be amenable to other diagnostic x-ray applications.
Generally, CT scanners have included a floor-mounted frame assembly which remains stationary during a scan and a rotatable frame assembly mounted therein. An x-ray tube is mounted to the rotatable frame assembly which rotates around a patient receiving examination region during the scan. Radiation from the x-ray tube traverses the patient receiving region and impinges upon an array of radiation detectors. Using the position of the x-ray tube during each sampling, a tomographic image of one or more slices through the patient is reconstructed.
The x-ray tube assembly includes a housing within which a rotating anode x-ray tube is mounted. High voltage and control leads pass through the housing to the tube. During x-ray generation, electrons are emitted from a heated filament in the cathode and accelerated to a focal spot area on the anode. Upon striking the anode, the focal spot is heated white hot to excite the emission of x-rays. Some portion of the electrons, or secondary electrons, strike the surrounding housing and are converted into undesirable waste heat. In fact, most of the energy applied to an x-ray tube is converted to heat. One of the persistent problems in CT scanners and other radiographic apparatus is effectively and efficiently dissipating the waste heat created while generating x-rays.
In order to remove the waste heat, a cooling oil is circulated between the housing and the x-ray tube. The oil is typically drawn from an output aperture located at one end of the housing, circulated through a heat exchanger on the rotating gantry and returned to an inlet aperture in the opposite end of the housing. The returned, cooled fluid flows axially through the housing toward the outlet aperture, absorbing heat from the x-ray tube. Transferring the heat removed by the heat exchanger from the rotating gantry is logistically difficult. The cooling of the x-ray tube is crucial to the life and quality of the tube. With the increasing demand of higher power CT x-ray tubes, the issue of cooling has become even more important and more difficult.
The power applied to an x-ray tube generally follows a designated duty cycle. As a result, the amount of the heat dissipation rate from the x-ray tube changes cyclically. To ensure sufficient cooling, an x-ray tube cooling system is generally designed based on the peak value of the heat dissipation received by the system. Thus, the volume of the cooling system may be unnecessarily large, but permitting the x-ray tube to become too hot during operation can irreversibly damage an expensive x-ray tube.
The present invention provides a new and improved cooling system for overcoming the above-reference drawbacks and others.
The present invention relates to an improved cooling system and method for effective and efficient removal of waste heat from a CT scanner.
In accordance with one aspect of the present invention, a diagnostic imaging system comprises an x-ray tube, an x-ray detector disposed across an imaging region from the x-ray tube, a cooling oil circuit which circulates cooling oil over the x-ray tube to remove heat form the x-ray tube, and a second cooling circuit which removes heat form the cooling oil circuit at a heat removal rate that is less than a heat generation rate of the x-ray tube.
In accordance with another aspect of the present invention, a cooling system for an x-ray tube of a diagnostic scanner is provided. The system comprises a cooling fluid that is in thermal contact with an x-ray tube and absorbs heat from the x-ray tube. The system also comprises a heat buffer which receives the cooling fluid after absorbing heat from the x-ray tube and a refrigeration system in thermal contact with the cooling fluid. The heat buffer contains a high heat capacity material in thermal contact with the cooling fluid passing therethrough. The refrigeration system removes heat from the cooling fluid before the cooling fluid returns to the x-ray tube.
In accordance with another aspect of the present invention, a radiographic cooling method is provided. The x-ray tube is intermittently operated to generate x-rays and heat. The heat generated by the x-ray tube is absorbed with a cooling fluid. A portion of the heat from the cooling fluid is absorbed in a heat buffer while the x-ray tube is generating x-rays and heat. The heated cooling fluid is cooled and the cooled cooling fluid is recirculated to the x-ray tube.
One advantage of the present invention resides in its ability to handle peak heat loads during the generation of x-rays, yet reduce the size of the heat retraction system needed to cool the cooling fluid.
Another advantage of the present invention is that it increases the efficiency of the system.
Another advantage of the present invention resides in its compactness, freeing valuable space on the rotating gantry.
Still other advantages and benefits of the invention will become apparent to those skilled in the art upon a reading and understanding of the following detailed description.